This invention relates to a method of processing a color photothermographic elements capable of dry thermal development that is sequentially compatible with traditional wet-chemical processing.
In conventional color photography, films containing light-sensitive silver halide are employed in hand-held cameras. Upon exposure, the film carries a latent image that is only revealed after suitable processing. These elements have historically been processed by treating the camera-exposed film with at least a developing solution having a developing agent that acts to form an image in cooperation with components in the film.
It is always desirable to limit the amount of solvent or processing chemicals used in the processing of silver-halide films. A traditional photographic processing scheme for color film involves development, fixing and bleaching, and washing, each step typically involving immersion in a tank holding the necessary chemical solution. By scanning the film following development, the subsequent processing solutions could be eliminated for the purposes of obtaining a color positive print. Instead the scanned image could be used to directly provide the color positive print.
By the use of photothermographic film, it would be possible to eliminate processing solutions altogether, or alternatively, to minimize the amount of processing solutions and the complex chemicals contained therein. A photothermographic (PTG) film by definition is a film that requires energy, typically heat, to effectuate development. A dry photothermographic film requires only heat. A solution-minimized photothermographic film may require small amounts of aqueous alkaline solution to effectuate development, which amounts may be only that required to swell the film without excess solution. Development is the process whereby silver ion is reduced to metallic silver and in a color system, a dye is created in an image-wise fashion. In all photothermographic films, the silver is retained in the coating after the heat development.
It can be difficult, however, to scan through imagewise exposed and photo processed silver halide films when the undeveloped silver halide is not removed from the film during processing. The retained silver halide is reflective and this reflectivity appears as density in a scanner. The retained silver halide scatters light, decreasing sharpness and raising the overall density of the film, to the point in high silver films of making the film unsuitable for scanning. High densities result in the introduction of Poisson noise into the electronic form of the scanned image and this in turn results in decreased image quality. Furthermore, the retained silver halide can printout to ambient/viewing/scanning light, rendering non-imagewise density, degrading signal-to noise of the original scene, and raising density even higher.
It is therefore an object of the present invention to improve the processing of dry-developed photothermographic film in which the film can be optionally processed by a traditional wet-chemical process in order to obtain a completely desilvered film for a higher quality print, archival film, and/or optical printing.
The present invention is directed to a method of processing color photographic film that has been imagewise exposed in a camera, said film having at least three light-sensitive units which have their individual sensitivities in different wavelength regions, each of the units comprising at least one light-sensitive silver-halide emulsion, binder, and dye-providing coupler, which method in order comprises: (a) thermally developing the film without any externally applied developing agent, comprising heating said film to a temperature greater than 80xc2x0 C. in an essentially dry process, such that an internally located blocked developing agent in reactive association with each of said three light-sensitive units becomes unblocked to form a developing agent, whereby the unblocked developing agent forms dyes by reacting with the dye-providing couplers to form a color negative image; (b) processing the developed film of step(a) by contacting it with a non-blocked developing agent, under agitation at a temperature of 30 to 50xc2x0 C. under aqueous alkaline conditions, without forming a color negative image in the film by reaction of the non-blocked developing agent with the dye-providing couplers inside the silver-halide emulsions, and (c) desilvering said film in one or more desilvering solutions to remove unwanted silver and/or silver halide, thereby forming a color negative image; and (d) thereafter forming a positive-image color print from the desilvered film;
In one embodiment of the present invention, the film comprises at least one blocked inhibitor that is released upon thermal development which inhibitor has substantially no effect in dry thermal development such that development proceeds in the usual manner, and wherein when the thermal development and concomitant release of the inhibitor precedes the wet-chemical process, the effect in the wet-chemical process is such that no development occurs. However, the use of the blocked inhibitor may improve image discrimination, but is not essential, to the practice of the present invention. According to the present invention, the photothermographic film can be thermally developed, even exposed to light, and then re-developed through a C-41 type of process, including bleaching and fixing, resulting in an acceptable and stable image in the film for scanning or optical printing.
In one preferred embodiment, the film is backwards compatible with respect to thermal development and wet-chemical processing and comprises at least one blocked inhibitor that is released upon thermal development which inhibitor has substantially no effect in dry thermal development such that development proceeds in the usual manner, and wherein the wet-chemical process does not have the capability to release the inhibitor, so development also can proceed in the usual manner, but wherein when thermal development and concomitant release of the inhibitor precedes the wet-chemical process, the effect in the wet-chemical process is such that no development occurs.
Thermal activation preferably occurs at temperatures ranging from about 80 to 180xc2x0 C., preferably 100 to 160xc2x0 C. In one preferred embodiment of the invention, the photothermographic element comprises an effective amount of a thermal solvent. In another preferred embodiment of the invention, the photothermographic element comprises a mixture of organic silver salts (inclusive of complexes) at least one of which is a silver donor.